The present invention relates generally to power amplifiers and, more particularly, to switching power amplifiers such as of a type suitable for driving magnetic resonance imaging (MRI) gradient coils, for example.
Gradient coils in MRI systems require high, rapidly changing current as well as precise current control. To achieve fast current changes, a high voltage drive is needed, requiring high-voltage, high-current semiconductors (typically insulated gate bipolar transistors, i.e., IGBT's). Higher voltage devices generally have higher switching losses, limiting the maximum switching frequency attainable. With high switching losses, the time interval permitted for the high-voltage inverter to switch at a sufficiently high frequency to maintain precise current waveforms is also limited.
Accordingly, it is desirable to provide a switching amplifier that reduces and distributes device switching losses such that arbitrary waveforms can be maintained for extended periods of time, thereby enabling high-performance advanced imaging. It is also desirable to provide a switching amplifier having the flexibility and capability to supply gradient coils having different requirements (e.g., voltage, current and frequency). It is also desirable to provide such a switching amplifier with minimal filtering, output ripple, and amplifier losses.